Mobile Operators are expanding their network coverage by integrating various access-technology domains into a networked mobility core. A user equipment (UE, referring to a device used by an end-user to communicate) can access the 3rd Generation Partnership Project (3GPP) 5th generation (5G) mobile network and operator services through an access network based on wireless local area networking (i.e. Wi-Fi), or other radio access technology (RAT) types. There are standardized interfaces which provide a user plane with related control and mobility support, for instance, 3GPP S2a (specified in TS 29.275 and TS23.402) and S2b (specified in TS 29.274 and TS29.275) that define this interworking, and the same interfaces are inherited by the 3GPP 5G architecture. Specifically, the interfaces in 5G may have different names than their corresponding interfaces in 4G. However, the approach of accessing 3GPP services through a non-3GPP network such as IEEE 802.11 based Wireless LAN networks remains in 5G.
When the access network through which the UE attaches is a trusted access network (based on 3GPP S2a interface) there is interworking between the access and the home network, with mechanisms for exchanging user-location information (ULI) without UE involvement. However, for untrusted access network, there are no interfaces between the home network and the access network.